Bump up the generator version, which is exposed in SPV test results.

SPIRV/GlslangToSpv.cpp

@@ -8197,7 +8197,8 @@ int GetSpirvGeneratorVersion()
     // return 5; // make OpArrayLength result type be an int with signedness of 0
     // return 6; // revert version 5 change, which makes a different (new) kind of incorrect code,
                  // versions 4 and 6 each generate OpArrayLength as it has long been done
-    return 7; // GLSL volatile keyword maps to both SPIR-V decorations Volatile and Coherent
+    // return 7; // GLSL volatile keyword maps to both SPIR-V decorations Volatile and Coherent
+    return 8; // switch to new dead block eliminator; use OpUnreachable
 }
 
 // Write SPIR-V out to a binary file